1. Field of the Invention
This invention relates generally to apparatus and methods for treatment of wastewater and, more particularly, to apparatus and methods for aerobic treatment wastewater in a single tank employing an inverted cone clarifier.
2. Prior Art
Relatively small, self-contained wastewater treatment systems are being employed throughout the country for treatment of wastewater from domestic sources, particularly single family dwellings located in areas which are not sewed by a larger municipal collection and treatment system. Strict federal and state clean water standards have resulted in a proliferation of various units designed to produce an effluent which meets those standards. Most states require stringent testing of treatment systems proposed for sale. A relatively small number of small volume aerobic treatment systems have been approved for sale due to the inability to meet the required effluent standards. By far the most popular and accepted test standard is NSF Standard 40 for Individual Aerobic Wastewater Treatment Plants (revised in June of 1990), known as "NSF Standard 40 ", as developed by the NSF Joint Committee on Wastewater Technology. Proposed units are tested by NSF International at the NSF test facility in Chelsea, Mich.
One popular treatment system design employs a single cylindrical tank having an inverted cone clarifier positioned within the tank with four radially spaced air pipes delivering air into the tank outside of the clarifier, as illustrated in U.S. Pat. No. 4,650,577, invented by Mr. Bradley L. Hansel (hereafter referred to as the "inverted cone system"). The geometry of the inverted cone system has proven to be a cost effective and efficient way to treat domestic sewage. However, even these units and variations on the inverted cone system have had some difficulty meeting NSF Standard 40.
Prior art treatment units similar to the inverted cone system have attempted to improve performance by raising the dissolved oxygen content of the wastewater within the tank, thus providing additional support for the aerobic bacteria which feed on the waste. An example of such an attempt can be seen in U.S. Pat. No. 5,221,470, invented by Mr. Jerry L. McKinney. In this system, two air pipes deliver air to the lower portion of the tank and terminate at diffusers, which produce fine bubbles to maximize oxygen transfer to the wastewater. Such systems concentrate on oxygen transfer as opposed to mixing, leaving quiescent zones between air outlet pipes. However, an additional filter was required to attain proper treatment.
A modification of the inverted cone system was thus desirable to maintain the basic geometry of the system while increasing treatment efficiency.